Multiplex control system



July 29, 1947. w E. s. PURINGTQN w IIULTIPLEX comm; SYSTEM Filed Aug. 2, 1944 3 Sheena-Shea; S

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Patented July 29, 1947 2,424,900 MULTIPLEX coN'moL SYSTEM Ellison S. Purington, Gloucester, Mass assignor, by memo assignments, to Radio Corporation of America, New York, Delaware N. 1L, a corporation of Application August 2. 19, Serial No. 547,730

1 Thi invention relates to a signalling or control system responsive to recurrent pairs of pulses having predetermined time intervals between the individual pulses of each pair. The two pulses of each pair are propagated over different channels and signalling or control is eflected by sclecting the pulse sequence on the two channels and by selecting the intervals between pulses of each pair. One such system is set forth in my copending application Ser. No. 537,799, filed May 29, 1944, for Radio control system (II-777) wherein pulses are produced having 50, 100 or 150' microseconds delay between the pulses of each pair and provision is made to select the channel to be pulsed first. In this way six different controls are obtained although the number may be increased as desired. 7

The present invention provides a multiplex control system in which two such controls are obtained simultaneously. The controls may, for 2 1.

example, comprise left or "right rudder, "up" or down" and flash and secure." One control of each group may be sent simultaneomly with one control from the other group, i. e., "left and up, "right and up, "left and down," "right and down," so that all possible navigational changes are provided for. The additions] controls, such as flash and secure" may be used when navigational controls are not required.

For example flash may refer to the turning on of a light signal, and "secure" to locking of the course against further radio control.

In one embodiment this is accomplished by interleaving the pairs corresponding to the selectedcontrol sequences. For example, "right" rudder may be responsive to a pulse a on channel h followed in microseconds by a pulse b on a channel 12, left rudder to pulse a on channel 11 followed in microseconds by pulse b on channel f2 and flash to pulse a on channel I: folfor example the "up sequence in an alternating series. The receiver segregates the two sets of pulses and actuates the control circuits in accordance therewith.

The invention will be better understood by referring to the following description, taken in con,

2 nectlon with the accompanying drawings in which a specific embodiment has been set forth for purposes of illustration.

In the drawing Figure 1 is a schematic diagram of a transmitting circuit embodying the invention, Figures 2 to 7 inclusive are pulse diagrams which illustrate the procedure for deriving the pulses for controls R and D from the rapid variations of grid voltage in two triodes of a multivibrator, Figures 8 to 11 inclusive are pulse diarams which illustrate the manner in which time delay circuits provide two time separated pulses from a single pulse, Figures 12 and 13 are pulse diagrams which illustrate pulses which are combined and Figure 14 is a pulse diagram which 11-- lustrates the combined propagated pulses. Similar reference characters are, applied to similar elements throughout the drawings. The pulse diagrams have exa gerated scales only for the purpose of facilitating an understanding of the operation of the device.

In Figure 1, a multivibrator in determines the rate of recurrence of the pairs of pulses and causes the pairs of pulses for one set of operations to occur at different time from the other pairs of pulses for the other operation. This multivibrator comprises two triodes ii, iii, the cathodes of which are connected by a line 2H! to the grounded negative end of a driving battery 2", and the anodes of which are connected to the positive side of battery 200 through resistors l3, M respectively and line 2| i. Resistors I5 and II are connected from the grids of triodes i I and II to ground lead m and condensers ll, it are connected respectively from the plate of each triode to the grid of the other triode.

A pulse forming and amplifying circuit 2|! comprises two triodes 2i and 22, with cathodes connected to the negative lead 2"], and with anodes connected through resistors 23 and 24 to positive lead 2. A resistor 25 is connected from the grid of triode 22 to ground lead 2I0, a condenser 28 is connected from the anode of triode 2! to the grid of triode 22 and one end of an output condenser 21 is connected to the plate of triode 22.

The constants of themultivibrator circuit II] are so chosen that the multivlbrator oscillates for example at a fundamental rate of 100 vibrations per second. Referring to Figs. 2 and 3, at

the instant tube H starts to draw current due to the grid potential rising from a value below cutoff to a more positive but still negative value, the plate voltage of tube II is lowered due to the voltage drop in resistor 13, which due to the coupling condenser Il drives the grid of tube I2 negative, increasing the potential of the anode of tube I2 due to the reduced current in resistor the grid of tube II going positive and ends by v causing the grid of tube II to go more positive it is seen that the operation or tube I I is such as to accelerate its grid in its positive swing until limited by grid current. As a result the positive swing of the grid of tube II through the region of conduction is very rapid, and at the same time the grid of tube I2 is likewise driven rapidly negative to a value far beyond cutofl. Upon readjustment of the voltage across condenser II in a discharge circuit comprising elements II, II, 200 and I6, the grid of tube I2 returns positively and when conduction starts, a chain of events starts which drives the grid of tube II rapidly negative without grid current limitation.

As a result of the multivibrator operation, the grid oi'triode 2I which is connected to the grid of tube I I abruptly changes from below cut oil to cathode potential once per oscillator cycle, and abruptly changes from cathode potential to below cutoif also once per oscillator cycle, thereby tending to produce a current of square wave form with very abrupt sides in the plate resistor 23. With a lull cycle multivibrator, tor example, the space current through triode H "can change from zero to maximum value in the order of 1 microsecond, and can change'in the reverse sense in a similar very small period of time.

The time constant of the circuit comprising condenser 26, resistors 23 and 25, tube 2I and battery 200 is such that the condenser 26 adjusts itself to a change of plate current very rapidly.

pressed on output condenser I21. The positive Pulses on condensers 21 and I2! are alternate however as they are derived from opposite potential positions of the multivibrator circuit I0.

It should be noted that differences in multivibrator tube characteristics (shown in Figs. 2 and 3), are compensated by the limiting action of circuits 22 and I22 (as shown in Figs. 4 and 6).

The output of circuit 23 is impressed through the output condenser 21 upon an artificial line comprising inductors 28 in series with suitable mutual inductance between successive inductor elements, condensers 26 connected across the input and output oithe inductor elements to a ground lead 2I2 and condensers 30 connected from junctions of the inductor elements to ground lead 2I2. This line is terminated with a resistor 3| connected across the output condenser 29. The number of sections of this line may be many more than here shown. This line is so designed that a pulse, shown in Fig. 5, entering from condenser 21 is transmitted along the line and absorbed in the terminating resistor 3|, creating voltage pulses at points 23, 34 and 35 of substantially the same characteristics but with centers of the pulses at points 33, 34 and 35 occurring substantially 50, 100 and 150 microseconds later,

This is accomplished by choosing the values resistors 23 and 25 and the capacity of condenser 26 to be suitably small. As a result, when the tube 2| suddenly passes its maximum current the potentials 01' both ends of condenser 26 are driven suddenly negative, carrying with it the grid of tube 22 as shown in Fig. 4. But condenser 26 rapidly discharges to its new lowered equilibrium voltage allowing the grid of triode 22 to return to ground potential. That is, a negative pulse of short duration, say the order of microseconds is produced on the grid of triode 22 immediately as the result of tube II starting to Pass current. A half cycle later (assuming a sym-- metrical oscillatory circuit), when tube I2 suddenly passes current, the grid of tube 2| is driven negatively, tending to produce a positive pulse on the grid of tube 22, but this is minimized by the current flow to the grid of tube 22, and the increased speed of readjustment of the voltage of condenser 26. As a result, a positive pulse of short duration is impressed from the plate circuit of tube 22 upon the output condenser 27, followed a half cycle later by a smaller negative pulse. These positive pulses are subsequently utilized, but the negative pulses are subsequently suppressed.

A circuit I including triodes HI and I22 and output condenser I21 is similar to the circuit 22 above described, and the grid voltage on tube I22 is shown in Fig. 6. The corresponding parts have been given similar reference numbers but increased by I00 to avoid duplicating the descriptlon thereof.

The operation of circuit I2ll driven from the grid of tube I2 is similar to that of circuit 22, resulting in a positive pulse of short duration imrespectively, than the center of the pulse at input point 22. The first section of the line is provided inpart to insure similarity of the first pulse of the series to the later pulses. The construction and operation of the line operated from the output of tube I22 is similar to that from the output of tube 22 and has been given similar reference numbers but increased by I 06. The voltage on capacitor I2! is shown in Fig. 7.

For selecting the time delay for operations for which a pulse on frequency {1 is to be radiated first, and a later pulse is to be radiated on frequency h, three double pole single throw switches are supplied, operatively connected to transmission line points 22, 33,34 and 35 by conductors including resistors 26, 31, 38 respectively. These switches may in practice constitute the output devices or magnetic relays operated by remote control push buttons, but are here shown in simpleat possible form. One of the movable blades of each switch, terminated at points 39, 4B and 4|, is connected through resistor 36 to initial pulse point 32. The other blades of the three switches are individually connected from terminals 42, 43, 44 to the later points 33, 34, 35 on the transmission line through individual resistors 31, II and a direct connection respectively. The drawing shows switch It closed for establishing "right" operation with the pulse on channel is delayed 50 microseconds behind that on 11. Switches L (left) and F (flash) are open.

The output switch terminals 45, 48, 41 are joined in, parallel by bus bar SI and also the terminals 43, 43, 52 are Joined in parallel by bus bar 52. Similar connections are made for the switches U, D and S for operations up," down" and secure, designated by numbers I00 greater than for switches for operations R, L and F.

It is apparent that a pulse will be established across from bus bar M to ground for the initial pulse regardless of which switch R, L or F is closed, as shown in Fig. 8, but that a pulse will be established selectively from bus bar 52 to ground at a later time with the amount of delay determined by the choice of switch, as shown in Fig. 9.

Clipping and combining tubes 53 and 54 are for providing pulses for channel {1 and similarly purposed tubes I53 and IE4 for channel f2. Tubes 63 of channel is.

. 2I3. The tubes I53 and I54 and resistors I55 and I56 are similarly connected. The grid of tube 53 is joined to bus bar -I to be driven by the undelayed pulses, shown in Fig. 8, corresponding to operations R, L and F, and the grid of tube 54 is connected to the bus bar I52 to be driven by the delayed pulses, shown in Fig. 9, for operations U, D, S. The grids of tubes I53 and I54 are correspondingly connected to bus bars I5I and 52, to receive the delayed and undelayed pulses, shown in Figs. and 11, respectively, for the operation The cathodes of all four tubes 53, I53, 54, I54 are joined together, and are connected through resistor 2M to line 2I4aconnected to the positive end of battery 288, and through resistor 282 paralleled by bypass condenser 283 to the grounded lead 2I3. Output resistors 51 and I51 are connected from the positive lead 2I4a to the paralleled plates of tubes 53 and 54, and the paralleled plates of tubes I53 and I58 respectively. a

In the operation, the constants are so chosen that the tubes 53, I53, 54, I54 are all biased beyond cutoff due to the current flow through resistor 2M and resistor 282 to ground. Therefore these tubes will be actuated only in response to those parts of the voltage pulses delivered through the switches which have instantaneous values above a predetermined amount as shown by the clipping levels of Figs. 8 to 11. In this manner undesired parts of the wave form including the negative pulses on the transmission lines are suppressed, and only pulses with fiat bases subsequently appear in the output resistor. Thus a negative pulse with base line at the positive voltage value of battery 280 is produced in the plate resistor 51 both from the initial pulse at point 32.

due to closure of switch R, and from the delayed pulse from point I34 due to closure of switch D. Similar pulses for channel is are developed in the plate resistor I51. The values of the resistors 35, 31, 38, I36, I31, I38 are so chosen that the width of the pulses appearing in resistors 51 and I 51 are substantially the same regardless of the point on the pulse delay circuit from which the pulse is derived.

The plates of tubes 53 and 54 are connected through condenser 59 to the grid of triode 81 which is in turn connected to a ground lead 2I4 through a resistor 83. The cathode of tube BI is connected to ground lead .2I4, the plate is connected through resistor 65 to lead 2 I5 connected to the positive end of battery 208, also through condenser'61 to a resistor 89 the other end of which is connected to ground lead 2 I4, and a resistor 1I the other end of which is connected to the grid of a triode 1'5, and also to the anode of a diode 13 the cathode of which is connected by a line 2I6 to the positively biased cathodes of clipper combiner tubes 53 and 58. The plate of triode is connected through a resistor 11 to the positive lead 2 I 5 and also through a condenser 8| to a negative pulse terminal 85. The cathode of triode 15 is connected through a resistor 13 to ground lead 2I4 and also through a condenser 88 to a positive pulse terminal 81. The amplifier for channel h is similarly arranged as above stated with parts given corresponding reference numbers increased by I80.

In operation, the negative voltage pulses in plate resistor 51 for operation of channel h are 6 impressed upon the grid of triode GI, and amplifled and positive pulses are impressed from the plate of tube 6i upon the limiter 13 which limits the voltage impressed upon triode 15 to the peak value determined substantially by the voltage drop in the positive biasing resistor 202. By use of the tube 15 these positive pulses are amplified to produce a negative voltage pulse at high impedance at terminal 85 and a positive voltage pulse at terminal 81, shown in Fig. 12, either of which may be utilized as may Le desired for operation of the radio transmitter for channel f1. Similar pulses are produced at terminals I55 and I81, shown in Fig. 13, for actuating transmitter Thus when switch R is closed as shown, an I undelayed pulse a derived from point 32 is fed through tubes 53, GI and 15 to terminal or 81 to be propagated on channel f1 followed in 50 microseconds by a pulse b derived from point 33 which is fedthrough tubes I54, I8I and I15 to terminal I85 or I81 to be propagated on the channel is, as shown in Fig. 14. If switch L or F is closed instead of the switch R. the same sequence will occur but the delay will be or microseconds respectively. These two pulses will be repeated at the frequency of the multivibrator l8.

With the switch D closed as shown, an-undelayed pulse derived from the point I32 is fed through the tubes I53, I6I and I15 to the terminals I85 and I81 to be propagated on the'channel fa followed in 100 microseconds by a pulse derived from the point I34 which is fed through the tubes 54, GI and 15 to-be propagated on the channel f1. With the switches U or S closed instead of the switch D the same sequence will occur except that the pulses will be separated by A receiver of the type described in my copending application above mentioned may be used to receive the'pulses and will be selective of the two pulse sequences to actuate the corresponding control circuits. The two selected controls may thus be operated simultaneously as above described.

' Although a specific embodiment of the invention has been set forth for purposes of illustration it is to be understood that various changes and modifications may be made as will be apparent to a person skilled in the art. The invention is only to be restricted in accordance with the following claims. I

What is claimed is:

1. In a multiplex interleaved control system, the improvement comprising a pulse forming circuit to form two series of recurrent pulses with the pulses of the two series occurring alternate- 1y, a separate delay circuit fed by each series of pulses having output terminals pulsed in predetermined time sequence to form recurrent pairs of pulses corresponding to the individual pulses of each series, a pair of transmission channels,

and means supph'ing the individual pulses of each pair to the respective channels.

2; In a multiplex interleaved control system, the improvement comprising a pulse forming circuit to form two series of recurrent pulses with the pulses of the two series occurring alternately, a separate delay circuit ied by each series of pulses having output terminals pulsed in predetermined time sequence to form recurrent pairs of pulses corresponding to the individual pulses oi each series, a pair of transmission channels, means supplying the individual pulses of each pair to the respective channels, and means controlling the sequence of the pulses of each pair on the two channels.

3. In a multiplex interleaved control system, the improvement comprising a pulse forming circuit to form two series of recurrent pulses with the pulses of the two series occurring alternately, a separate delay circuit fed by each series of pulses having output terminals pulsed in predetermined time sequence to form recurrent pairs of pulses corresponding to the individual pulses of each series, a pair of transmission channels, means controlling the timing of the pulses of each recurrent series of pairs, and means supplying the individual pulses of each pair to the respective channels in opposite time sequence.

4. In a multiplex interleaved control system, the improvement comprising a pair of delay circuits, means pulsing the inputs of the delay circuits at the same rate of recurrence but at alternate times, the interval between successive pulses being greater than the maximum time delay of said delay circuits, 9. pair of transmission channels, and means pulsing each channel irom selected points on eachdelay circuit.

5. In a multiplex interleaved control system, the improvement comprising a pair of delay circuits, means pulsing the inputs of the delay circuitsat the same rate of recurrence but at alternate times, the interval between successive pulses being greater than the maximum time delay of said delay circuits, a pair of transmission channels, means pulsing each channel from selected points on each delay circuit. and control means to select the points in accordance with the desired, time sequence of said pulses.

6. In a multiplex interleaved control system, the improvement comprising a pair of pulse delay circuits, an Oscillator circuit to produce a series of pulses at a predetermined rate having a pair of output points at which said pulses occur alternately, means supplying pulses from each point to one of said delay circuits so that successive pulses progress through alternate delay circuits, a

pair of transmission channels, and selective 8 means connecting each channel to be fed by pulses from selected points oneach delay circuit. '7. In a multiplex interleaved control system, the improvement comprising a pulse forming circult to form two series of recurrent pairs of pulses of the two series occurring alternately, controlling the time spacing between the pulses of each pair in each series, propagating the individual pulses of each pair of one series over separate transmission channels in a given sequence and propagating the individual pulses of each pair of the other series over said transmission lines in the opposite sequence.

9. The method of deriving pulses for multiplex control which comprises producing two series of recurrent pairs of pulses with the pairs of pulses of the two series occurring alternately, controlling the time spacing between the pulses of each pair in each series, and propagating the individual pulses of each pair over separate transmission channels.

10. The method of deriving pulses for multiplex control which comprises producin two series of recurrent pairs of pulses with th pairs of pulses of the two series occurring alternately, controlling the time spacing between the pulses of each pair in each series, propagating the individual pulses of each pair over separate transmission channels, and utilizing the transmitted pulses of each series in accordance with their sequence for selective control.

\ ELLISON S. PURINGTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,009,946 Powell July 30, 1935 2,349,810 Cook May 30, 1944 FOREIGN PATENTS Number Country Date 132,453 Austria Mar. 25, 1933 

